Treatment of hides and skins



Patented Jan. 7, 1941 UNITED STATES 2,228,133 TREATMENT ornmns AND SKINSArthur M. Breach, Frame, England, assignor to Hall Laboratories, Inc.,Pittsburgh, Pa., a company of Pennsylvania No Drawing. ApplicationOctober 13, 1939, Se-

rial No. 299,353. In Great Britain October 11,

2 Claims.

leather from skins, light hides and the like, and has for its object theprovision of a method of treatment in which the somewhat crude anduncertain process of puering or bating asipracticed for many years issuperseded by a neater and cleaner operation, and one that affordsopportunity for accurate yet easy control.

As is known, the process of puering or bating follows the successiveoperations of de-wooling or unhairlng, liming, splitting, washing anddeliming, and is usually followed by washing, scudding, washing,drenching and pickling.

As is well known, the object of puering or bat ing is to render theskins, and the resulting leather, soft and supple. Skins which haveundergone the liming process must be thoroughly freed of lime beforetanning, and for light and soft leathers must be reduced or brought downso that the elasticity or resilience of the skin fibers is got rid of,so that the skin, when tanned, can be stretched without springing back.These objects have hitherto been achieved by, passing the skins throughan infusion of dung, or an enzyme bate. The operation of drenching,frequently carried out in the manufacture of light leathers, has similarobjects, viz: the ultimate production of a soft and stretchy leather. Itwill be seen, therefore, that the effects achieved by the puering,bating and/or drenching processes are entirely different in every wayfrom the process of tanning, which has for its object the conversion ofskin tissue into an imputrescible and permanent material known asleather.

According to the present invention, the results ordinarily obtained bypuering or bating is produced by the use of a water solublemetaphosphate in conjunction with a suitable acid of which sufficient isused to produce a final pH of about 2.6 of both liquor and goods, andwithout the aid of bacteria or hating enzymes, such as are essentials inthe already known excremental puers or artificial bates. Furthermore, bymy process the use of the drenching process may be avoided.

The term water-soluble metaphosphates includes alkali metal and ammoniumhexametaphosphates, with or without trimeric metaphosphates and/orpyrophosphates and/or polyphosphates.

A satisfactory concentration of the salt in the solution for my purposein accordance with the present invention is one per cent, and asatisfactory quantity of the solution to use is three times the weightof skins being treated.

This invention relates to the manufacture of 7 The bath used accordingto the present invention may start neutral and be brought to the pHvalue of about 2.6 gradually, for which purpose organic and/or inorganicacids may be used. If desired, salts such as sodium chloride may also beadded for their buffering and antiseptic value.

The known process of puering, depending as it does upon the action ofbacteria, enzymes, and the chemical constituents naturally present indung, is an uncertain, and moreover disgusting,

process and, furthermore, one which may rightly be regarded as anuisance by neighboring residents on account of its obnoxious smell.

Dung, as received from kennels, varies very considerably in composition;furthermore, the process, as commonly practiced, is influencedconsiderably by atmospheric and climatic changes, No proper standardsexist to determine whether or not the skins are sufficiently puered, andconsequently the operators discretion and experience have to be reliedupon in order to ensure the goods getting accurate treatment. The onlypractical tests available, in order to determine whether or note skin issufilciently puered or bated, is feel and to some extent, appearance.According to the kind of. silkiness and freedom from harshness orgristle, a decision has to be made as to whether the skin has hadsufficient treatment.

By reason of the lack of concrete standards, and the fact that theoperator's judgment may be frequently at fault, many errors arise in theexcrementalpuering process. Furthermore, the skins comprising a parcelfor treatment, numbering perhaps 240 skin's, react in different wayswith the dung, some yielding very much quicker than others, some havingto receive very pro longed treatment before they are in a fit condition.It is frequently found that skins which are sufficiently puered or batedon the sides are still hard on the backs, and such skins yield mostirregular and unsatisfactory results in the finished leather. Cocklyskins, especially, demand prolonged treatment, and are then frequentlyunsatisfactory when tanned.

Insufficient puering causes the production of a harsh and discoloredleather, While over-puering leads to holes and weakness in the valuablegrain surface. The process of puering, at best, is accompanied byconsiderable loss of skin substance. As much as 1.254 gms. skinsubstance per litre has been found in a puer liquor after normal use;this amount would be much greater with excessive puering, but even thisquantity is equivalent to 1% on the dry ash free skin. The ordinaryfeel, by which is meant a Gil process of puering, if carried to onlyslight excess, destroys the hyaline or glassy layer of the grainsurface; such skins when tanned possess a dull, hungry, and open etchedappearance.

Much that has been said of excremental puers may be applied toartificial bates. In practice they are no less offensive, as it iscustomary, in order to obtain maximum bating eiiiciency, to use a stockliquor and to strengthen it for each successive pack. Although a freshbating liquor is free from bacteria and is dependent entirely uponenzyme action, together with chemical delimlng, for its efficiency, thepractice of using such a liquor repeatedly results in it becomingbacterially active. The action of a freshly made hate is much slowerthan that of a dung liquor, and in some cases, unless the action isstrengthened by the use of old stock liquor, or by the addition of aquantity of dog dung, the degree of softness or flacciclity obtainableis insufficient.

Whereas a dung puer is three-fold in action, viz: bacterial, enz-ymicaland chemical, a freshly made bate liquor is twofold, viz: enzymical andchemical. As this liquor becomes older, and thus bacterially active, oris assisted by the addition of dung, the action is speeded up. Underunfavorable conditions, or through lack of judgment on the part of theoperator, such bating liquors will give rise to the same faults as areexperienced in the puering operation proper, such as damaged grain,excessive loss of skin substance, and tenderness.

Indeed, it may be said that cockly sheepskins and goat skins, which areby nature harsh and in consequence require a very thorough softening,are-frequently inadequately depleted by a fresh bate liquor, or if so,only after very prolonged treatment. The increased and quicker action,brought about by the use of stock solutions, or by the addition ofexcrement, bring the relationship of the puer liquor and the bacteriallyactive enzyme bate liquor very close, certainly as far as liability toerrors is concerned, such as grain damage, loss of skin substance, andweakness.

Having given a brief description of the dung and enzyme bates, togetherwith some account of their shortcomings and the difficulties in applyingthem in such a way as to ensure uniform results .in the finishedleather, I will set out the advantages of the present invention, asfollows:

(a) Complete freedom from obnoxious odors.

(b) Consequent easier disposal of waste liquors.

(c) A neater and more positive process than is offered by either dung orenzyme bates.

(d) A process easily controlled, and not requiring the services orexperience 01' a skilled puerman.

(e) A process which affects all skins in the parcel under treatmentequally, and which is productive of the necessary uniform results withina definite time, as opposed to the erratic results produced by the dungand enzyme bates, and to the uncertain period required for their properperformance.

(f) A process which cleanses the skins under treatment and whichsolubilizes any lime and magnesium soap present in the goods as a resultof the previously performed processes, so much so that the operation ofscudding, as ordinarily performed for this purpose, may be dispensedwith.

(g) A process which affords the necessary depleting action, yet which atthe same time conserves skin substance and strength, and preserveseffectively the hyaline or glassy layer of the grain surface of theskin.

(h) A process which, applied to washed and delimed skins and lighthides, functions as a bate, washing and/or cleansing agent, a drench anda pickle, and which produces in a few hours the results at presentobtained by the lengthy sequence of operations of 'deliming, washing,puering or hating, washing, drenching, washing, and pickling; in fact,my process does in, say three hours, in one operation, the workordinarily performed by means of the named older fashioned processes inabout twelve to eighteen hours. Y

(i) A process which is neater, simpler, and cheaper, on account of theelimination of the skilled labor ordinarily employed in the deliming,washing, puering or bating, washing, drenching and pickling operations,and which saves by reason of the elimination of these processes,considerable handling.

(9) A process which reduces the cost of the results ordinarily obtainedby puering or hating,

washing, drenching, washing and pickling by more than and which iscapable of easy application without requiring the services of anexperienced puerman or chemist.

(k) A process by which skins and light hides may be brought to theproperly depleted, cleansed and pickled condition, and in which thegoods may be kept until required for tanning.

Having set out the advantages of the present process, I will now give anexample of how to carry it into practice. Limed sheep or lamb grains,limed sheep or lamb pelts, or such like limed skins are washed inrunning water until the wash liquor is clear of lime, and then carefullydelimed by any suitable means to pH '7.

The operation or softening the hides and skins is carried out in ashelved drum, rotating 'preferably at about 18 R. P. M. I

A 1% solution of sodium metaphosphate is carefully prepared and fed intothe drum in quantity equal to three times the weight of the delimedgoods to be treated. The goods are then treated in the drum by rotatingthe latter for one hour, after which time the pH of the goods and liquoris gradually reduced to about pH 2.6 by the several cautious additionsof diluted sulphuric or other suitable acids.

When equilibrium has been reached (i. e. the pH value 2.6 has beenestablished substantially throughout the bath and the goods themselves)an addition of 10% sodium chloride is made, and drumming continued for afurther period of half an hour. The goods are then ready for tanning,using salt in the tanning liquor in the usual way and as is customarywhen processing pickled stock.

When processing hard natured stock, such as goat skins, it isadvantageous to commence the operation at a temperature of 80 F. and toprolong it before making the addition of salt. During the drummingprocess, however, it is necessary to avoid too high a temperature, andto this end the drum should be stopped occasionally and ventilated byremoving the door.

The invention is not limited to the preferred example but may beotherwise embodied or practiced within the scope of the followingclaims.

I claim:

1. The process of softening limed hides and skins prior to tanning,which comprises delimthem to pH about 7, drumming them with a soiu-.

tion containing a. water soluble metaphosphate and having a pH of about7, said drumming being continued for a period of about one hour,

thereafter reducing the pH of the solution to about 2.6 and continuingthe drumming for a period oi about half an hour, the .combined' drummingtreatments with metaphosphate solution before and after making itstrongly acid rendering the hides and skins in a soft flaccideom ditionso that when tanned they can be stretched without springing back.

ARTHUR M. BREACH.

